Power tools are known which are provided with a continuously variable rotary dial to control a function of the power tool. For example, the rotational speed and hammer frequency of a hammer drill can be controlled by turning a rotary dial, thereby varying the resistance of a variable resistor. A hammer drill of this type is disclosed in U.S. Pat. No. 4,454,459.
However, such tools suffer from the disadvantage that impacts on the dial, for example as a result of a user dropping the tool, can cause damage which can be expensive to repair. In particular, if the tool should be dropped onto its speed adjustment dial, the impact force can be transmitted down a shaft attached to the dial and into the variable resistor, causing further damage to the electrical components of the tool, which significantly increases the cost of repair of the tool.
Preferred embodiments of the present invention seek to overcome one or more of the above disadvantages of the prior art.